help, help, help! 4L65E tranmission problem! please help!

[stok2shok]

No check engine light, but security light flashes on. Truck (2002 Yukon Denali XL) shifts in 1st & 2nd only. Revs up to 4k rpm (took foot of gas to prevent damage), but still ddoesn't engage 3rd or 4th. Hooked up scan tool & no dtc's given. What could it be?

Thanks

[ScarabEpic22]

Sounds like your trans is done to me.

Security light could mean you need to have the PCM sync'ed to the BCM, did you try and different tune or replace anything lately?

[stok2shok]

Sounds like your trans is done to me.

Security light could mean you need to have the PCM sync'ed to the BCM, did you try and different tune or replace anything lately?

I haven't done anything but get it to my driveway. It drove fine in first and second earlier, but now it barely makes it through first gear.

[IJ.]

Dead 3/4 pack, can happen if the shifter is left in D and you kick down to 2nd under load. :(

3/4 pack can't exhaust fast enough so is still partially engaged when 2nd locks in, 3/4 loses.

[ScarabEpic22]

I haven't done anything but get it to my driveway. It drove fine in first and second earlier, but now it barely makes it through first gear.

I meant, what did you do PRIOR to having this? If nothing is the answer, your trans is toast. Sorry to be the bearer of bad news, the 60/65/70E family is pretty dang weak when you start throwing big power at it. Heck they blow all the time in stock applications.

[joecar]

Concur with 3/4 clutch pack... but did you check fluid level/condition anyway...?

What vehicle mods...?